1. Technical Field
The present invention relates to a display device, and more particularly, to a display device which can suppress an occurrence of an afterimage phenomenon.
2. Discussion of the Related Art
A liquid crystal display is one of the most widely used flat panel displays. For example, the liquid crystal display is commonly found in a variety of electronic devices such as flat screen televisions, laptop computers, cell phones, and digital cameras.
The liquid crystal display includes two substrates provided with field-generating electrodes such as pixel electrodes and a common electrode and a liquid crystal layer interposed therebetween. The liquid crystal layer includes liquid crystal molecules having optical anisotropy and dielectric anisotropy. The liquid crystal display displays images by applying voltages to the field-generating electrodes to generate an electric field in the liquid crystal layer. The electric field determines orientations of the liquid crystal molecules in the liquid crystal layer to adjust polarization of incident light.
However, when voltages having the same polarity are continuously applied to liquid crystal molecules, the liquid crystal molecules are degraded, and thus, a direct current (DC) bias accumulates and remains in a liquid crystal layer. The residual DC bias may transform a subsequent data voltage or produce an undesirable electric field in the liquid crystal layer even when no data voltage is supplied. To prevent the degradation of liquid crystal molecules, an inversion driving method for inverting the polarity of a voltage applied to a liquid crystal layer was developed.
Inversion driving includes frame inversion driving in which the polarity of a common voltage is inverted in units of frames, line inversion driving in which the polarity of the common voltage is inverted in units of gate lines when each gate line is scanned, dot inversion driving in which the polarity of the common voltage is inverted in units of pixels, etc. However, even though inversion driving is performed, a DC bias still remains in a liquid crystal layer due to a change in a kickback voltage, etc.
Meanwhile, ionic impurities, together with liquid crystal molecules, are floating in a liquid crystal layer. The ionic impurities are adsorbed to electrodes of upper and lower display panels due to a residual DC bias in the liquid crystal layer, thereby distorting the electric field in the liquid crystal layer. The distortion may cause an afterimage to appear on a screen. The afterimage is a phenomenon that occurs when an image of a previous frame remains without completely fading out to influence an image of a current frame.
Accordingly, there is a need for a liquid crystal display that is capable of suppressing the occurrence of an afterimage phenomenon that results from the concentration of ion impurity in the liquid crystal layer.